1. Field of the Invention
This application concerns an improved fuel injector for an internal combustion engine with superior fuel preparation characterized by very fine atomization of the fuel. Introduction to the engine of very small fuel particles promotes good fuel economy and reduced exhaust emissions. Poor fuel preparation or atomization is a common problem with prior fuel injectors and the atomization quality is particularly poor upon opening of the injector's valve. The subject injector produces fine fuel atomization throughout the entire valve opening/closing event.
2. Description of Related Art
In fuel injection design, an objective is good fuel preparation with production of a spray consisting of fine fuel particles. Prior injector designs have been found to be incapable of consistently generating a spray with such small fuel particles over the entire opening/closing valve event and especially when the valve first opens. Particularly when the valve in these prior injectors is first opened, it has been found that the particle size is relatively large. The subject injector has achieved good fuel atomization, that is, particle size of ten microns or less even when the valve first opens.
It has been recognized previously that good fuel preparation or atomization is desirable particularly at the beginning of the injector valve's opening. An early example of injector design theory is found in the U.S. Pat. No. 1,252,254 to Fisher disclosing a mechanically controlled fuel control device as opposed to the subject electrically controlled fuel injector. The Fisher design provides for a constant flow through the device even when the valve is closed. The aim is to improve fuel preparation particularly as the valve first begins to open. In Fisher, the valve movement from a closed position to a more opened position is by a lever which is actuated by an undisclosed device associated with operation of the engine, probably a cam.
The Fisher patent teaches us that by maintaining continuous fuel movement, fuel atomization is improved. It is known that a still liquid which is suddenly acelerated by, for example, a Valve opening, will not be initially finely atomizied. As previously mentioned, fuel in the Fisher device constantly flows through an annular chamber upstream of the valve. Then when the valve is opened, the already moving fuel passes to the outlet and is discharged from the injector in a fine spray. Even when the Fisher valve is closed, fuel is passed through the annular chamber and is routed back to the fuel tank through a groove and several passages formed in the valve. Without the above described continuous flow through the Fisher device, a significant quantity of stagnant fuel would accumulate above the outlet when the valve is closed. Subsequently, when the valve opened, a relatively large volume of fuel would decend in a mostly axial direction to the outlet and be discharged in the form of relatively large droplets.
Thus we see that to achieve good atomization of fuel in the Fisher device, a contant flow of fuel is made to pass therethrough. When the valve is opened, the fuel is discharged from the outlet of the device. However when the valve is closed, the flow must have an alternative route. This route is through a groove and passages formed in the valve. This alternative route must be blocked when the valve is open in order to maintain fluid pressure in the device. Accordingly, the groove is so located that upward movement of the valve causes a sleeve to cover the groove effectively severing the alternate route. This arrangement of the groove and sleeve and their spacing would be very critical and difficult to achieve particularly in a high pressure device. Therefore, such an arrangement in the subject device would be unwelcome and perhaps unworkable due to the required precise axial locating of the groove relative to the sleeve as well as close tolerances between the members. The required return tubing and so forth is also undesirable.
The subject fuel injector is electrically actuated and electronically controlled. It is a pulse width modulated type in which a valve moves from a normal closed position to an opened position in response to energization of a coil of an electric solenoid. The quantity of delivered fuel is determined by the length of time the coil is energized. This length of time which the coil is energized is determined by action of an electronic control unit or computer which responds to several engine and vehicle parameters or input signals. A primary objective of the subject electronically controlled injector is superior fuel preparation, namely fuel atomization characterized by very fine particles right from the opening of the injector valve through valve closure. This has been achieved by production of a spray pattern with fuel paricles with an average particle size of ten microns or less right from the initiation of valve opening to the closing of the valve.